1. Field of the Invention
The present invention relates to a polymeric-resin-coated papermaking-processing belt, such as that used to transfer a paper sheet between sections, or between elements of a given section, such as the individual presses in a press section, of the paper machine on which it is being manufactured, or to carry the sheet into other processes. Specifically, the present invention relates to a papermaking-processing belt having a base with a polymer coating on one side and a needled web on the other side.
2. Description of the Prior Art
Sheet transfer belts are designed both to carry a newly formed paper sheet through a portion of a paper machine, so as to eliminate open draws from the machine, and to release the sheet readily to a paper machine fabric, such as a press fabric or dryer fabric, or to another rotating element, such as a press roll or transfer roll, at some desired point in the machine. By definition, an open draw is an interval where the paper sheet passes from one component of the paper machine to another over a distance greater than the length of the cellulose fibers in the sheet without any support from a papermaker's fabric. By way of contrast, a closed draw is an interval where the paper sheet passes across such a distance supported by a papermaker's fabric or belt. The elimination of open draws removes a major cause of unscheduled paper machine shut-down, the breakage of the newly formed, and consequently weak, sheet at an open draw.
To work successfully, a sheet transfer belt must perform three critical functions on the paper machine: a) to remove the paper sheet from a press fabric without causing sheet instability problems; b) to cooperate with a press fabric in one or more press nips to ensure optimal dewatering and high quality for the paper sheet; and c) to transfer the paper sheet in a closed draw from one press in the press section to a sheet-receiving fabric or belt in the next press, or presses, in the press section, or to a dryer fabric in the dryer section.
A sheet transfer belt which successfully carries out these critical functions is disclosed in commonly assigned U.S. Pat. No. 5,298,124, entitled "Transfer Belt" and issued on Mar. 29, 1994, the teachings of which are incorporated herein by reference. The transfer belt disclosed therein has a surface topography characterized by a pressure-responsive, recoverable degree of roughness, so that, when under compression in a press nip, the degree of roughness will decrease, thereby permitting a thin, continuous water film to be formed between the transfer belt and a paper sheet to bond the paper sheet to the transfer belt upon exit from the press nip. When the original degree of roughness returns sometime after exit from the nip, the paper sheet may be removed from the transfer belt, perhaps with the assistance of a minimal amount of vacuum or suction, to a permeable fabric, such as a dryer fabric.
The sheet transfer belt disclosed in U.S. Pat. No. 5,298,124 comprises a reinforcing base with a paper side and a back side, and has a polymer coating, which includes a balanced distribution having segments of at least one polymer, on the paper side. The balanced distribution takes the form of a polymeric matrix which may include both hydrophobic and hydrophilic polymer segments. The polymer coating may also include a particulate filler. The reinforcing base is designed to inhibit longitudinal and transverse deformation of the transfer belt, and may be a woven fabric, and, in addition, may be endless or seamable for closing into endless form during installation on the paper machine. The reinforcing base may have one or more fiber batt layers attached by needling to its back side.
The fiber batt layer or layers, which may also be referred to as a needled web, are attached to the back side of the reinforcing base to control the impregnation of the polymer coating into the reinforcing base from the paper side during the manufacturing process. During the life of the transfer belt on a paper machine, the needled web protects the load-bearing yarns of the reinforcing base from damage by abrasion.
In practice, however, the needled web tends to hold paper particles during operation on a paper machine. Unfortunately, normal cleaning methods, such as the use of high-pressure water sprays during machine stoppages, have proven to be ineffective in removing the paper particles. As a consequence, paper particles build up on the surface of the needled web and become matted thereinto in the form of pill-like clumps of fiber and paper. These clumps tend to stick to stretch rolls and the like, which, in turn, pull them from the surface of the needled web along with some of the underlying needled web itself, thereby exposing the load-bearing yarns of the reinforcing base.
Moreover, larger clumps adhering to the surface of the needled web may cause the polymer coating on the paper side of the transfer belt, and possibly the reinforcing base itself, to be damaged by a surface doctor blade which is permanently fixed adjacent to a stretch roll or the like and cleans the paper side of the transfer belt running therearound. A larger clump of fiber and paper, carried on the inside, needled-web surface of the transfer belt and passing through the fixed gap separating the surface of the roll from the surface doctor blade, raises the transfer belt toward the surface doctor blade, which, being fixed, can then abrade or cut into the belt.
The object of the present invention is to remedy this situation by providing a transfer belt having a needled web on its inner surface, which needled web does not have a tendency to hold paper particles and is readily cleanable by normal cleaning methods.